1. Field of the Invention
This invention relates to a rotary head drum arrangement of the helical scanning type which is applied most suitably, for example, to a video tape recorder for a broadcasting station.
2. Description of the Prior Art
A rotary head drum arrangement of the helical scanning type applied to a video tape recorder for a broadcasting station is already known and disclosed, for example, in Japanese Patent Laid-Open Application No. 58-6547.
An exemplary one of such conventional rotary head drum arrangements is shown in FIG. 3. Referring to FIG. 3, the conventional rotary head drum arrangement includes a rotary drum D, and a pair of first video recording heads (called paired heads) A REC1 and B REC1, a single first erasing:head E1, a pair of first audio recording and reproducing heads A APB1 and B APB1, a pair of first video reproducing heads A PB1 and B PB1, a pair of second video recording heads A REC2 and B REC2, a single second erasing head E2, a pair of second audio recording and reproducing heads A APB2 and B APB2, and a pair of second video reproducing heads A PB2 and B PB2 arranged in an angularly equidistantly spaced relationship by an angle of 45 degrees from each other on an outer periphery of the rotary drum D. The pair heads in each head pair are spaced by an angular distance of 6 degrees from each other.
The rotary drum D is rotated at a high speed in the direction indicated by an arrow mark a, and during such rotation of the rotary drum D, the heads thereon helically scan a magnetic tape T wound helically on the rotary drum D and a fixed drum (not shown) to effect recording or reproduction of a desired image and/or a desired sound.
With a rotary head drum arrangement of the type described above, where a tape entering point (point at which a head is brought into contact with the magnetic tape) of the rotary drum D is represented by P1: a tape leaving point (point at which the head is brought out of contact with the magnetic tape) of the rotary drum D is represented by P2; a starting point (switching position) of recording or reproduction is represented by SW0.degree.: and an ending point (switching position) of recording or reproduction is represented by SW180.degree. as shown in FIG. 3, when a video signal is to be written, upon recording, onto the magnetic tape T over an angle of 180 degrees of the rotary drum D, seven velocity errors (phase errors) are produced, at each of the tape entering point P1 and tape leaving point P2, on a recording track influenced by an impact error due to hitting of heads upon the magnetic tape T in the order in time of t1 to t9 as seen from FIG. 4.
Here, in the conventional rotary head drum arrangement, each of the heads REC1, REC2, PB1, PB2, APB1 and APB2 is constructed from a pair of heads, that is, pair heads A and B while each of the erasing heads E1 and E2 is constructed from a single head.
Accordingly, the phase of hitting of the erasing head E1 or E2 upon the magnetic head T does not match with the phase of hitting of any of the pair heads between upon recording and upon reproduction as seen from FIG. 4. Since the velocity of propagation of an impact error is higher than the relative velocity of the heads, the conventional rotary head drum arrangement has a problem that a time base error on a reproduction signal is so great as to produce a great impact error in a reproduction output so that a deformation or color irregularity takes place with a reproduction screen.